kernel/rcupdate.c

   1 /*
   2  * Read-Copy Update mechanism for mutual exclusion
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright IBM Corporation, 2001
  19  *
  20  * Authors: Dipankar Sarma <dipankar@in.ibm.com>
  21  *          Manfred Spraul <manfred@colorfullife.com>
  22  *
  23  * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
  24  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  25  * Papers:
  26  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
  27  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
  28  *
  29  * For detailed explanation of Read-Copy Update mechanism see -
  30  *              http://lse.sourceforge.net/locking/rcupdate.html
  31  *
  32  */
  33 #include <linux/types.h>
  34 #include <linux/kernel.h>
  35 #include <linux/init.h>
  36 #include <linux/spinlock.h>
  37 #include <linux/smp.h>
  38 #include <linux/interrupt.h>
  39 #include <linux/sched.h>
  40 #include <linux/atomic.h>
  41 #include <linux/bitops.h>
  42 #include <linux/percpu.h>
  43 #include <linux/notifier.h>
  44 #include <linux/cpu.h>
  45 #include <linux/mutex.h>
  46 #include <linux/export.h>
  47 #include <linux/hardirq.h>
  48
  49 #define CREATE_TRACE_POINTS
  50 #include <trace/events/rcu.h>
  51
  52 #include "rcu.h"
  53
  54 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  55 static struct lock_class_key rcu_lock_key;
  56 struct lockdep_map rcu_lock_map =
  57         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  58 EXPORT_SYMBOL_GPL(rcu_lock_map);
  59
  60 static struct lock_class_key rcu_bh_lock_key;
  61 struct lockdep_map rcu_bh_lock_map =
  62         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
  63 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
  64
  65 static struct lock_class_key rcu_sched_lock_key;
  66 struct lockdep_map rcu_sched_lock_map =
  67         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
  68 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
  69 #endif
  70
  71 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  72
  73 int debug_lockdep_rcu_enabled(void)
  74 {
  75         return rcu_scheduler_active && debug_locks &&
  76                current->lockdep_recursion == 0;
  77 }
  78 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
  79
  80 /**
  81  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
  82  *
  83  * Check for bottom half being disabled, which covers both the
  84  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
  85  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
  86  * will show the situation.  This is useful for debug checks in functions
  87  * that require that they be called within an RCU read-side critical
  88  * section.
  89  *
  90  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
  91  */
  92 int rcu_read_lock_bh_held(void)
  93 {
  94         if (!debug_lockdep_rcu_enabled())
  95                 return 1;
  96         if (rcu_is_cpu_idle())
  97                 return 0;
  98         return in_softirq() || irqs_disabled();
  99 }
 100 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 101
 102 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 103
 104 struct rcu_synchronize {
 105         struct rcu_head head;
 106         struct completion completion;
 107 };
 108
 109 /*
 110  * Awaken the corresponding synchronize_rcu() instance now that a
 111  * grace period has elapsed.
 112  */
 113 static void wakeme_after_rcu(struct rcu_head  *head)
 114 {
 115         struct rcu_synchronize *rcu;
 116
 117         rcu = container_of(head, struct rcu_synchronize, head);
 118         complete(&rcu->completion);
 119 }
 120
 121 void wait_rcu_gp(call_rcu_func_t crf)
 122 {
 123         struct rcu_synchronize rcu;
 124
 125         init_rcu_head_on_stack(&rcu.head);
 126         init_completion(&rcu.completion);
 127         /* Will wake me after RCU finished. */
 128         crf(&rcu.head, wakeme_after_rcu);
 129         /* Wait for it. */
 130         wait_for_completion(&rcu.completion);
 131         destroy_rcu_head_on_stack(&rcu.head);
 132 }
 133 EXPORT_SYMBOL_GPL(wait_rcu_gp);
 134
 135 #ifdef CONFIG_PROVE_RCU
 136 /*
 137  * wrapper function to avoid #include problems.
 138  */
 139 int rcu_my_thread_group_empty(void)
 140 {
 141         return thread_group_empty(current);
 142 }
 143 EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 144 #endif /* #ifdef CONFIG_PROVE_RCU */
 145
 146 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 147 static inline void debug_init_rcu_head(struct rcu_head *head)
 148 {
 149         debug_object_init(head, &rcuhead_debug_descr);
 150 }
 151
 152 static inline void debug_rcu_head_free(struct rcu_head *head)
 153 {
 154         debug_object_free(head, &rcuhead_debug_descr);
 155 }
 156
 157 /*
 158  * fixup_init is called when:
 159  * - an active object is initialized
 160  */
 161 static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 162 {
 163         struct rcu_head *head = addr;
 164
 165         switch (state) {
 166         case ODEBUG_STATE_ACTIVE:
 167                 /*
 168                  * Ensure that queued callbacks are all executed.
 169                  * If we detect that we are nested in a RCU read-side critical
 170                  * section, we should simply fail, otherwise we would deadlock.
 171                  * In !PREEMPT configurations, there is no way to tell if we are
 172                  * in a RCU read-side critical section or not, so we never
 173                  * attempt any fixup and just print a warning.
 174                  */
 175 #ifndef CONFIG_PREEMPT
 176                 WARN_ON_ONCE(1);
 177                 return 0;
 178 #endif
 179                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 180                     irqs_disabled()) {
 181                         WARN_ON_ONCE(1);
 182                         return 0;
 183                 }
 184                 rcu_barrier();
 185                 rcu_barrier_sched();
 186                 rcu_barrier_bh();
 187                 debug_object_init(head, &rcuhead_debug_descr);
 188                 return 1;
 189         default:
 190                 return 0;
 191         }
 192 }
 193
 194 /*
 195  * fixup_activate is called when:
 196  * - an active object is activated
 197  * - an unknown object is activated (might be a statically initialized object)
 198  * Activation is performed internally by call_rcu().
 199  */
 200 static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 201 {
 202         struct rcu_head *head = addr;
 203
 204         switch (state) {
 205
 206         case ODEBUG_STATE_NOTAVAILABLE:
 207                 /*
 208                  * This is not really a fixup. We just make sure that it is
 209                  * tracked in the object tracker.
 210                  */
 211                 debug_object_init(head, &rcuhead_debug_descr);
 212                 debug_object_activate(head, &rcuhead_debug_descr);
 213                 return 0;
 214
 215         case ODEBUG_STATE_ACTIVE:
 216                 /*
 217                  * Ensure that queued callbacks are all executed.
 218                  * If we detect that we are nested in a RCU read-side critical
 219                  * section, we should simply fail, otherwise we would deadlock.
 220                  * In !PREEMPT configurations, there is no way to tell if we are
 221                  * in a RCU read-side critical section or not, so we never
 222                  * attempt any fixup and just print a warning.
 223                  */
 224 #ifndef CONFIG_PREEMPT
 225                 WARN_ON_ONCE(1);
 226                 return 0;
 227 #endif
 228                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 229                     irqs_disabled()) {
 230                         WARN_ON_ONCE(1);
 231                         return 0;
 232                 }
 233                 rcu_barrier();
 234                 rcu_barrier_sched();
 235                 rcu_barrier_bh();
 236                 debug_object_activate(head, &rcuhead_debug_descr);
 237                 return 1;
 238         default:
 239                 return 0;
 240         }
 241 }
 242
 243 /*
 244  * fixup_free is called when:
 245  * - an active object is freed
 246  */
 247 static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 248 {
 249         struct rcu_head *head = addr;
 250
 251         switch (state) {
 252         case ODEBUG_STATE_ACTIVE:
 253                 /*
 254                  * Ensure that queued callbacks are all executed.
 255                  * If we detect that we are nested in a RCU read-side critical
 256                  * section, we should simply fail, otherwise we would deadlock.
 257                  * In !PREEMPT configurations, there is no way to tell if we are
 258                  * in a RCU read-side critical section or not, so we never
 259                  * attempt any fixup and just print a warning.
 260                  */
 261 #ifndef CONFIG_PREEMPT
 262                 WARN_ON_ONCE(1);
 263                 return 0;
 264 #endif
 265                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 266                     irqs_disabled()) {
 267                         WARN_ON_ONCE(1);
 268                         return 0;
 269                 }
 270                 rcu_barrier();
 271                 rcu_barrier_sched();
 272                 rcu_barrier_bh();
 273                 debug_object_free(head, &rcuhead_debug_descr);
 274                 return 1;
 275         default:
 276                 return 0;
 277         }
 278 }
 279
 280 /**
 281  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 282  * @head: pointer to rcu_head structure to be initialized
 283  *
 284  * This function informs debugobjects of a new rcu_head structure that
 285  * has been allocated as an auto variable on the stack.  This function
 286  * is not required for rcu_head structures that are statically defined or
 287  * that are dynamically allocated on the heap.  This function has no
 288  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 289  */
 290 void init_rcu_head_on_stack(struct rcu_head *head)
 291 {
 292         debug_object_init_on_stack(head, &rcuhead_debug_descr);
 293 }
 294 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 295
 296 /**
 297  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 298  * @head: pointer to rcu_head structure to be initialized
 299  *
 300  * This function informs debugobjects that an on-stack rcu_head structure
 301  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 302  * function is not required for rcu_head structures that are statically
 303  * defined or that are dynamically allocated on the heap.  Also as with
 304  * init_rcu_head_on_stack(), this function has no effect for
 305  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 306  */
 307 void destroy_rcu_head_on_stack(struct rcu_head *head)
 308 {
 309         debug_object_free(head, &rcuhead_debug_descr);
 310 }
 311 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 312
 313 struct debug_obj_descr rcuhead_debug_descr = {
 314         .name = "rcu_head",
 315         .fixup_init = rcuhead_fixup_init,
 316         .fixup_activate = rcuhead_fixup_activate,
 317         .fixup_free = rcuhead_fixup_free,
 318 };
 319 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 320 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 321
 322 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 323 void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
 324 {
 325         trace_rcu_torture_read(rcutorturename, rhp);
 326 }
 327 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 328 #else
 329 #define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 330 #endif